Heart disease is the leading cause of death in most industrialized nations. Health care is able to treat and manage cardiovascular illnesses in a surprisingly effective fashion. However, the prerequisite is that the persons at risk are identified. Various tests have been developed, but due to the dire consequences of the disease, it is well worth the effort to continue the refinement of the methodology with which the risk for a cardiac death may be assessed.
Electrical instabilities in the heart are known to characterize or indicate a potential for abnormal conditions, which may result in sudden cardiac death (SCD). Sudden cardiac death is defined as an unexpected natural death from a cardiac cause within a short time period, generally ≦1 h from onset of symptoms, in a person without prior condition that would appear to result in instantaneous fatality. The majority of SCD events are associated with a structurally diseased heart. It has been estimated that only 3 to 10% of patients who have an out-of-hospital cardiac arrest are successfully resuscitated.
For decades, early repolarization (ER), which is characterized by an elevation of the junction between the end of the QRS complex and the beginning of the ST segment (i.e. J-point) from baseline on standard 12-lead electrocardiography (ECG, EKG), has been considered to be an innocuous finding in healthy persons, see Klatsky et al Am J Med 2003 115: 171-177.
The prevalence of ER in the general population varies from less than 1% to 13%, depending on age, race, sex, and the criterion for J-point elevation. Earlier, diagnosis of ER has not been considered relevant to the proposed prognosis in case of healthy subjects.
However, the presence of this pattern in leads other than V1 through V3 (especially in the inferior leads) has recently been associated with vulnerability to ventricular fibrillation in independent case-control studies, see Haissaguerre et al N Engl J Med 2008 358: 2016-2023, Nam et al N Engl J Med 2008 358: 2078-2079, and Rosso et al J Am Coll Cardiol 2008 52: 1231-1238. Furthermore, it is not clear whether all types of ER in inferior and/or lateral leads are associated with increased risk of life-threatening arrhythmias.